For the sake of simplicity, the invention is described using the most frequently used cement foam as an example of the production of such structural foams. The invention is, however, not to be limited to such cement foams. At the present time, the following procedure is usually employed for such structural foams.
To begin with, a foam is produced from air, water and a foaming agent, generally with the help of perforated disks arranged in series. This foam is supplied to a mixing apparatus at the mixing site. Over an additional pipeline, the pre-mixed cement slurry is brought into the mixing apparatus. When processing a cement foam in the upper floor of a house, the apparatus for producing the cement slurry and the foaming agent are usually on the first floor. This makes it necessary to force the heavy cement slurry to the top with the help of screw conveyors or the like. A further difficulty of the method used until now lies therein that, by mixing the pre-mixed foam with the cement, only so-called heavy foam with foam weights of 800 kg/cm.sup.3 or more can be produced.